The United States and Japan will step up their defence cooperation to deal with the threat from nuclear-armed North Korea as tensions in East Asia remain high, officials from the two allies said on Thursday.

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He said another West Australian on their radar was Junaid Thorne, who spoke at Islamic centres in Sydney and Melbourne around the new year as part of a lecture tour backed by a radical organisation known as Millatu Ibrahim.

His brother Shayden was in a Saudi prison for terrorism-related offences at the time but was granted clemency in February and flew back to Perth.

"There hasn't necessarily been a law enforcement response that has been necessary out of that but it's the responsibility of security services to at least keep an eye on it and be able to recognise if there's been an escalation in what's being said or any actual physical reaction," Mr Harris-Hogan said.